He succeeded his brother Ecgberht I in 673. He must have come into conflict with Mercia, since in 676 the Mercian king Æthelred invaded Kent and caused great destruction; according to Bede, even churches and monasteries were not spared, and Rochester was laid waste.

Hlothhere's rule survived this onslaught, however. He appears for a time to have reigned jointly with his nephew Eadric, son of Ecgberht I, since a code of laws still extant was issued under both their names. In 685, Eadric went into exile and led the South Saxons against Hlothhere, who was defeated and died of his wounds.

The above information is derived from Bede, but Hlothhere is the earliest Kentish king for whom genuine charters survive. One charter [2] known from a 15th-century copy, is precisely dated to 1 April 675 in the first year of Hlothhere’s reign, which conflicts with accession date attributed to him by Bede. The charter of 679 survives in its original form.[3] Two further charters attributed to Hlothere (S1648, S1648a), appear to have been altered copies of charters of Swæfheard (S10[4]) and Swæfberht (S11[5]) (Kelly 1995). A law code, the Law of Hlothhere and Eadric, is jointly attributed to him and his successor Eadric.